1. Field of the Invention
The present invention relates to a reproducing circuit of a wobble signal recorded on a recordable disk of an optical disk.
2. Description of the Related Art
At present, a write once optical disk such as a CD-R/DVD-R, and a recordable optical disk such as a CD-RW/DVD-RW or DVD-RAM, in addition to a read-only optical disk such as a CD or a DVD-RAM, are put on the market. At the time of recording of these recordable optical disks, clock signal generation from a reproduction signal, which is performed in a conventional read-only disk, can not be performed. Thus, a groove as a portion where information is recorded on a disk is wobbled at a constant period, and a clock signal at the time of recording is generated from a wobble signal obtained by reproducing this wobbling (hereinafter referred to as wobble) by a push-pull system.
FIG. 2 shows a conventional example of a wobble signal reproducing circuit. Reflected light from a laser spot irradiated on a disk forms a far field pattern 2 on an optical detector 1 divided in two. Two outputs of the optical detector are subtracted by a subtracting circuit 17 to take out a push-pull component. From the obtained push-pull signal, a wobble frequency is extracted by a band pass filter (BPF) 18. A wobble signal reproduced from a CD-R/RW is a continuous signal of a frequency of 22.05 KHzxc2x11 KHz. In the CD-R/RW, since address information called ATIP (Absolute Time In Pregroove) is superimposed on the wobble signal by FM modulation, it has a width in frequency band. FIG. 3 is a view showing a disk surface of a DVD-R/RW. Reference numeral 301 in the drawing designates a groove in which data is recorded and which is wobbled similarly to the CD-R/RW. A wobble signal reproduced in the DVD-R/RW is a continuous signal of a single frequency of 140.65 KHz different from the CD-R/RW, and address information is not superimposed. Instead thereof, a pit called a land pre-pit (hereinafter referred to as an LPP) designated by 302 is recorded in a land portion which is between a groove and a groove and in which information is not recorded. The LPP exists in a region from the head of maximum amplitude position of a wobble to the third, and address information is recorded by this three bits.
In order to stably extract the wobble signal from the push-pull signal, it becomes necessary to reduce leakage of an RF signal to the push-pull signal. Thus, as disclosed in Japanese Patent Unexamined Publication No. Hei. 8-194969, it is conceivable that an automatic gain control circuit (AGC circuit) is provided at a front stage of the subtracting circuit of FIG. 2.
Besides, in recent years, as the capacity of a disk is increased, doubling of the speed of disk reproduction becomes active.
In double speed reproduction, it becomes necessary to change over the pass band of the BPF of wobble in connection with the double speed. As a method of causing this connection, although it is conceivable that setting of the pass band of the BPF is changed over by a microcomputer according to the reproducing speed of a disk, since access to the microcomputer becomes necessary each time the speed is changed, the processing becomes troublesome. In the case where CAV reproduction is performed with an increase in speed of disk reproduction, a deviation in band setting of the BPF occurs by the restriction on the number of accesses to the microcomputer, and this becomes a factor of a drop in S/N of the wobble signal and an increase in clock jitter due to that. With respect to this problem, as disclosed in Japanese Patent Unexamined Publication No. Hei. 11-203681, it is conceivable to use pass band automatic tracking by a dummy filter and a phase comparison circuit.
As set forth above, in the case where double speed reproduction of various disks is realized by one optical disk reproducing device, since the specifications of the respective disks are different, various problems occur. The problems of a wobble signal reproducing circuit are as follows:
1. Leakage of a Land Pre-pit Signal of a DVD-R/RW into a Wobble Signal
Here, in the case where the AGC (AUTOMATIC GAIN CONTROL) circuit is disposed at the front stage of the subtracting circuit of FIG. 2 as disclosed in Japanese Patent Unexamined Publication No. Hei. 8-194969, at the time of reproduction of a DVD-R/RW, an LPP signal leaks into an RF signal, and an AGC (AUTOMATIC GAIN CONTROL) gain is varied in accordance with the amplitude variation. Thus, there is a fear that the RF signal at the time of passing through the LPP leaks into the wobble signal.
2. The Processing for Lack of a Wobble Signal in an Address Information Region of a DVD-RAM
FIG. 4 is a view showing a disk surface of a DVD-RAM. Reference numeral 403 in the drawing designates a groove; and 404, a land. In order to raise recording density, the DVD-RAM adopts a land groove recording system in which signals are recorded in both the groove 403 and the land 404. Thus, address information in the DVD-RAM is recorded in a staggering manner with respect to respective tracks of the land and the groove as indicated by 401 and 402 of the drawing. The portion where the address information is recorded is called a PID (Physical Identification Data) region.
Although a wobble signal reproduced in the DVD-RAM has a single frequency of 157 KHz similarly to the DVD-R/RW, since the address information is recorded in the staggering manner in the PID region, when a push-pull component is detected and is subtracted, it lacks a signal at one side before the subtraction. Thus, similarly to the above item 1, in the case of considering provision of the AGC (AUTOMATIC GAIN CONTROL) circuit at the front stage of the subtracting circuit, it is conceivable that the AGC (AUTOMATIC GAIN CONTROL) is saturated in the PID region.
Besides, the wobble signal reproduced in a CD-R/RW has a band width, and the amplitude is varied. In order to reduce an offset due to that at binarization at a later stage, as disclosed in Japanese Patent Unexamined Publication No. Hei 11-161961, it is conceivable that an AGC (AUTOMATIC GAIN CONTROL) circuit is provided at a later stage of the BPF 18. However, in the DVD-RAM, since the groove does not exist in the PID region, it lacks the wobble signal at the time of reproduction of the PID region. Thus, similarly to the above, it is conceivable that this AGC (AUTOMATIC GAIN CONTROL) circuit is saturated in the PID region.
3. BPF Pass Band Setting
In the technique disclosed in Japanese Patent Unexamined Publication No. Hei 11-203681, there are a problem of accuracy of wobble signal band detection in the dummy filter and the phase comparison circuit, and a problem that a circuit scale is increased in order to improve the accuracy of the circuit. In the case where band setting of the BPF is made to follow a clock signal reproduced from a wobble signal, it becomes a problem that a ratio of a wobble signal frequency to a clock frequency is different according to the kind of a disk.
Like this, since the specifications of the wobble signals are different according to the disks, there has been a problem that in the case where the wobble signal reproducing circuits corresponding to the respective disks are provided, a circuit mounting area is increased.
In order to solve the above problems, in a wobble signal reproducing circuit for reproducing a wobble signal recorded by wobbling a groove formed on a disk, the wobble signal reproducing circuit includes an arithmetic circuit for calculating a push-pull signal, a band pass filter for extracting a wobble frequency component from an output of the arithmetic circuit, an AGC (AUTOMATIC GAIN CONTROL) circuit disposed at a front stage or inside of the arithmetic circuit, and land pre-pit detection means for detecting a land pre-pit region where a pit is formed in a land portion which is between the groove and a groove and in which information is not recorded, and a structure is such that a gain of the AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed over by a detection signal of the land pre-pit detection means at a time of reproduction of the land pre-pit region.
Besides, there is provided address information recording region detection means for detecting an address information recording region where an address is formed in a portion in which the groove is divided on a track into a land portion, and a structure is such that a gain of the AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed over by a detection signal of the address information recording region detection means at a time of reproduction of the address information recording region.
Further, there is provided a second AGC (AUTOMATIC GAIN CONTROL) circuit at an output of the band pass filter for extracting the wobble signal from the push-pull signal, and a structure is such that a gain of the AGC (AUTOMATIC GAIN CONTROL) circuit and a gain of the second AGC (AUTOMATIC GAIN CONTROL) circuit are fixed or a response time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit and a response time constant of the second AGC (AUTOMATIC GAIN CONTROL) circuit are changed over at a time of reproduction of the address information recording region.
Besides, there is provided means for detecting a scratch or a finger print of a disk to be reproduced, and a structure is such that a gain of the AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed by an OR operation output of a detection signal of the means and a detection signal of the land pre-pit detection means.
Further, a structure is such that a gain of the AGC (AUTOMATIC GAIN CONTROL) circuit and a gain of the second AGC (AUTOMATIC GAIN CONTROL) circuit are fixed or a response time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit and a response time constant of the second AGC (AUTOMATIC GAIN CONTROL) circuit are changed by an OR operation output of a detection signal of means for detecting a scratch or a finger print of a disk to be reproduced and a detection signal of the address information recording region detection means.
Besides, the land pre-pit detection means detects a land pre-pit recording region by a detection signal corresponding to a land pre-pit region position or the signal generated from the detection signal of the means and a clock obtained in synchronization with a rotation speed of the disk.
Further, the address information recording region detection means detects an address information recording region by a detection signal corresponding to an address information recording region position, the signal generated from the detection signal and a wobble signal, or the signal generated from the detection signal of the means and a clock obtained in synchronization with a rotation speed of the disk.
Besides, a pass frequency band of the band pass filter is substantially in proportion to a frequency of a clock obtained in synchronization with a rotation speed of the disk, and a proportionality coefficient between the pass frequency band and the frequency of the clock can be changed. Further, there are provided a scratch detection circuit for detecting a scratch or a finger print of the disk, and a function for fixing the pass frequency band of the band pass filter at a time of detection of the scratch.
Besides, there is provided a function in which a frequency of a clock obtained in synchronization with a rotation speed of the disk is measured and a pass frequency band of the band pass filter is fixed when the frequency is largely varied at a time of normal reproduction.
Besides, an arithmetic circuit for calculating a push-pull signal has a band for permitting a land pre-pit signal of a land pre-pit region to pass, and there is provided land pre-pit detection means for making the output of the arithmetic circuit the land pre-pit signal.
Further, a wobble signal reproducing circuit includes an arithmetic circuit for calculating a push-pull signal, a band pass filter for extracting a wobble signal frequency component from an output of the arithmetic circuit, and a subtracting circuit for subtracting an output of the band pass filter from the output of the arithmetic circuit, and a structure is such that the arithmetic circuit and the subtracting circuit have bands for permitting a land pre-pit signal of a land pre-pit region to pass, and there is provided land pre-pit detection means for making the output of the subtracting circuit the land pre-pit signal.